1. Field of the Invention
The present invention relates to a rear wheel suspension system in a vehicle suitable for attaining a reduction in weight of the vehicle and for increasing the degree of freedom in design and simplicity in construction.
2. Description of Background Art
As a rear wheel suspension system in a vehicle wherein a rear wheel axle side is secured to a rear portion of a vehicle body rollably through a roll shaft extending in the longitudinal direction of a vehicle body and vertically swingably through a swing shaft extending in the transverse direction of the vehicle body, and rear wheels are secured to a rear wheel axle, there is known, for example, a suspension system disclosed in Japanese Patent Laid-open No. Hei 5-39073 entitled xe2x80x9cSwing Type Vehicle.xe2x80x9d
FIGS. 10(A) to 10(C) of the above publication illustrate a swing type vehicle wherein a pair of right and left front wheels Wf, which are steered with a bar handle 2, are secured to a front portion of a body frame 1, a swing shaft 4 extending substantially
FIGS. 10(A) to 10(C) of the above publication illustrate a swing type vehicle wherein a pair of right and left front wheels Wf, which are steered with a bar handle 2, are secured to a front portion of a body frame 1, a swing shaft 4 extending substantially horizontally in the longitudinal direction of the vehicle body is provided in a rear portion of the body frame 1, a battery supporting frame 9 is coupled to a second swing shaft 75 which is coaxial with the swing shaft 4, a power unit P is connected to the swing shaft 4 through a swing joint 6, rear wheels Wr are secured to both ends of an output shaft of the power unit P, and a rear end of the battery supporting frame 9 and both right and left ends of the power unit P are connected together using two restriction rods 74R and 74L.
When the vehicle turns during high-speed travel, a large centrifugal force acts on the battery supporting frame 9 outwards with respect to the turning direction, so that with this centrifugal force the battery supporting frame 9 tilts outwards with respect to the turning direction, centered at the second swing shaft 75. With this tilting motion, a rear portion of the power unit P moves into the same direction as the direction where the centrifugal force acts, i.e., moves outwards with respect to the turning direction by the restriction rods 74R and 74L. Consequently, the power unit P tilts outwards with respect to the turning direction, centered at the swing joint 6, and the rear wheels Wr are steered inwards with respect to the turning direction, i.e., in the same direction as the front wheels Wf.
According to the above technique, the rear wheels are steered in the same direction as the turning direction (steering direction of the front wheels) with the centrifugal force acting on the battery supporting frame 9, a heavy object, with a battery 10 mounted thereon. Due to the necessity of mounting the heavy object on the rear portion of the vehicle body, it is difficult to attain the reduction in weight of the vehicle body and the degree of freedom in weight distribution is limited. Further, it is necessary to use the restriction rods 74R, 74L and connecting members such as ball joints attached to end portions of those restriction rods, resulting in that the number of components used increases and the manufacturing cost becomes high.
It is an object of the present invention to provide a rear wheel suspension system in a vehicle capable of reducing vehicle weight easily, increasing the freedom of vehicle design, and simplifying vehicle construction.
For achieving the above-mentioned object a vehicle with a pair of front and rear wheels is provided with a rear wheel suspension system connected to a joint member mounted in a rear portion of the vehicle body. The joint member includes a roll shaft extending substantially in the longitudinal direction of the vehicle body. The roll shaft is mounted so that a front end portion thereof is positioned lower than its rear end portion. Also provided is a vertical swing shaft extending in the transverse direction of the vehicle body, and a rear wheel support member for supporting rear wheels is connected to a rear portion of the joint member, thereby allowing the rear wheel support member to be secured to the vehicle body rollably and swingably.
Since it is not necessary to mount a heavy object on a rear portion of the vehicle body, it is possible to easily reduce the weight of the vehicle. In addition, the vehicle weight distribution can be set freely, and the degree of freedom for vehicle design can be improved. Further, rods for steering rear wheels and rod connecting members, as in the prior art, are no longer required. Thus, it is possible to simplify the construction of the rear wheel suspension system and to reduce the number of components used therein.
The joint member is provided with a bearing for supporting the roll shaft, and a damper is disposed between the roll shaft and the bearing. Since a damper is disposed between the roll shaft and the bearing, it is possible to easily adjust the rolling rigidity of the vehicle body and rear wheel steering characteristic, thus improving vehicle drivability.
The rear wheel support member can be combined with the vehicle drive source using the rear wheel axle as an output shaft. Further, the vehicle drive source, such as an engine or an electric motor, can also be combined with the rear swing arm, making it possible to reduce the number of components used and reduce the vehicle manufacturing cost.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.